Today's mobile applications and services display information to the user via a Graphical User Interface (GUI). Unfortunately, an attacker may tamper with that display, maliciously hiding, altering, or entirely fabricating display contents. User apps or the cloud services providing the information may be entirely unaware of the tampering. Mobile operating systems, such as Android and iOS, cannot guarantee the integrity and correctness of the app GUI content. This project is developing techniques to guarantee the integrity and correctness of security-sensitive GUI regions, to ensure that what a user sees in those regions is exactly what the app (or cloud service) intends to display. The researchers are developing the concept of a protected GUI region called a "viewport," which a cloud backend may statically associate with an app. The intent is to ensure that only the GUI of the application is able to display into the specified portion of the screen. The researchers are developing a viewport security enforcement monitor, using hardware features of the ARM processor, and developing programming and operating system support for viewports. The project exploits a synergy of hardware features, including virtualization, ARM TrustZone, and modern display controller with support for overlaid layers. Finally, the research team is evaluating the security assurance provided, performance overhead, and ease of use by application developers.